In effect, the air extracted from a spray booth contains, in suspension, two types of products which are in fact the constituents of the paint, lacquer or varnish:
solid compounds or pigments, PA1 volatile compounds or solvents representing 40% by weight of the product to be applied. PA1 a first gas flow containing the suspended compounds to be destroyed is channelled into a preheating unit; PA1 it is intimately mixed with a second uncontaminated gas flow constituting an external contribution; PA1 these two flows are combined and are recycled into a solvent captor in order to improve the yield of the desorption reaction; PA1 this flow, containing all the suspended components, is then subjected to a further preheating, which is more intense than the previous one, so that the pyrolytic oxidation reaction is complete; PA1 the gas flow, devoid of noxious particles, is cooled before being discharged to the environment.
Public authorities currently impose draconian standards on the amounts of air flowing through spray booths, both by extraction and intake; the situation is likewise for noise pollution.
It is common to encounter plants with flow rates of 20,000 m.sup.3 /h to 25,000 m.sup.3 /h; these flow rates which accrue over more than 20,000 registered plants carry overall 5000 tons of solvents annually.
Systems are known which are based on a simple trap containing active charcoal and on a single compact barrier, these systems only remaining functional if the volume of paint deposited corresponds only to a daily concentration which can be assimilated by this simple barrier.
In current plants, the majority of the solid compounds are trapped in dry or moist filters, whereas the volatile compounds are stored in active charcoal filters which have to be regenerated; nevertheless, the storage and regeneration process has the aim only of converting the heterogeneous discharges to homogeneous discharges in order to avoid the time of emissions of pollution peaks during the spraying stage, of storing the latter at 90% and of dispatching it to atmosphere at any time at a very low concentration (homogeneous discharges below the smell threshold and the threshold of toxicity risks for the neighborhood).
However, it is clear that the pollutions are quantitatively the same.